1. Field of the Invention
This invention relates to an image forming apparatus.
2. Description of Related Art
A conventional image forming apparatus has a fusing device fusing a developer image attached to a recording medium such as paper with heat applied to a fusing unit by a heat source. Where the paper wraps around the fusing unit during fusing due to some causes, the conventional image forming apparatus determines whether the paper wraps around the fusing unit based on the change in a temperature gradient of the fusing unit. Specifically, the conventional image forming apparatus determines that the paper wraps around the fusing unit where a temperature detection unit near the fusing unit detects a temperature equal to or less than a certain reference temperature or where a temperature gradient generated based on the temperature detected by the temperature detection unit exceeds a certain temperature gradient reference value. Un-examined Japanese patent application publication No. 2001-109319 describes such an image forming apparatus.
With the image forming apparatus thus structured, however, the temperature detection unit detects an abnormal temperature gradient where the temperature changes rapidly in a short time in a manner of spike noise due to occurrences of rapid changes in the fusing temperature. There raises a problem that the fusing device detects the remaining paper when detecting such an abnormal temperature gradient.